In regard to the processes for assembling semiconductor devices (hereinafter, also referred to as “semiconductor packages” or “packages”), the connection between an aluminum electrode of a semiconductor element (hereinafter, also referred to as “semiconductor chip” or “chip”) and the inner lead of a lead frame is currently achieved primarily by an electrical connection based on thermal compression of gold wires. Furthermore, in recent years, along with the market trend directed toward miniaturization, weight reduction and performance enhancement of electronic equipment, high integration and an increase in pin number of electronic components are in progress. Accordingly, there is a demand for wire bonding processes that are more complicated than before, and in the case of using a lead frame made of copper, it has been such that as the lead frame is exposed to a high temperature state at 200° C. to 250° C. for a long time period, oxidation of the copper surface proceeds even further.
Under such circumstances, even in the case of conventional semiconductor encapsulation materials that have excellent adhesiveness to an unoxidized copper surface, the semiconductor encapsulation materials often have poorer adhesiveness to copper in which oxidation has proceeded and the surface state is different. Thus, there are occasions in which peeling occurs at the interface between an encapsulating resin cured product and a lead frame at the time of die cutting after resin encapsulation molding or at the time of solder reflow.
Enhancing the adhesiveness between an insert article such as a lead frame and an encapsulating resin cured product in order to suppress peeling, contradicts the effect of enhancing the releasability of the encapsulating resin cured product from a molding mold. Therefore, there have been cases in which when the adhesiveness to an insert article such as a lead frame is enhanced, releasability from a molding mold is deteriorated, and thus moldability decreases.
Before the time when oxidation of a lead frame made of copper caused by high integration of electronic components caused a problem, a technique was suggested in which a polyethylene oxide wax and a semi-esterification product of a copolymer of a 1-alkene and maleic acid are added in combination as releasing agents in order to achieve a good balance between adhesiveness and releasability (see, for example, Patent Documents 1 and 2). According to this technique, although the adhesiveness to unoxidized copper and releasability are excellent, since a polyethylene oxide wax is used in combination, there is a problem that the adhesive power of the encapsulating resin to oxidized copper frames is decreased. Furthermore, when a semi-esterification product of a copolymer of a 1-alkene and maleic acid is used in combination with a non-oxidized polyethylene wax, the adhesive power is satisfactory, but there is a problem with releasability, such as trouble like cull sticking that occurs during continuous molding.